The Science of Aging and Running

Why your body slows and what you can do about it

Last spring, fresh into a new masters age group, I ran a 5K. Nothing unusual in that; I'd run spring 5Ks the year before ... and the year before that ... for quite a few years. The surprise was that I was 45 seconds faster than I'd been in any recent year. Age-graded, it was a massive PR.

Short course, I thought, but a couple weeks later, I did it again, then twice more. Friends were wondering about my training. "What are you doing differently?" they asked.

When I went back and looked at my training logs, the answer was surprising: I'd cut back my mileage. I'd done it simply because I was busy, but as the winter progressed, my speed workouts had responded. For masters runners, less is often more.

Aging, like injuries, is one of those things most of us prefer to deny. "It'll never happen to me," goes the common decree. But, as a non-running friend once said about her graying hair, "Consider the alternative." Eventually, we're all either going to become masters runners ... or not be runners. The options are limited.

Internet fountain-of-youth claims notwithstanding, the passage of years does indeed affect athletic performance. Last summer, the American College of Sports Medicine published a depressing litany of time's tolls: declining VO2 max, reduced strength, increased body fat, reduced lactic acid clearance, declining bone density and more. Not to mention heart disease, diabetes, arthritis and declining mental acuity. Put these together and, according to data compiled by World Masters Athletics, runners slow about 7 percent per decade in their 40s, 50s, and 60s (and more quickly after that).

The better we understand this process, the easier it is to beat the aging curve. Even if we merely reduce the rate at which the years affect our speed, that's a victory -- the runner's version of aging gracefully.

But it doesn't take a total revision of training philosophy. "You don't have to do a lot different," says Flagstaff, Ariz., coach and exercise physiologist Greg McMillan, himself a masters runner. "The physiological reactions in the body and the adaptations you want to get are the same." In other words, we merely have to modify how we do things, not what we do. For workout-addicted runners, that's good news.

VO2 Max

One indisputable effect of aging is declining aerobic horsepower. Classically, this is measured via VO2 max, your maximum rate of oxygen usage per unit of body weight. For sedentary people, VO2 max typically declines by about 10 percent per decade after age 30. For athletes who keep in training, the rate of decline can often be held to about half that.

Most runners associate this with reduced cardiac capacity. With age, there is a steady fall in the number of receptors in your heart muscle listening to the nervous system's signals telling it how fast to beat. As the heart becomes increasingly deaf to these messages, its maximum rate drops about one beat per minute each year. There also appears to be a decline in the heart's intrinsic ability to beat quickly. "It's not so much that the heart can't beat as quickly, though that's probably true," says Benjamin Levine of the University of Texas Southwestern Medical Center and Presbyterian Hospital in Dallas, Texas. "The heart can't relax as quickly. Out of all the factors that are probably an inevitable part of aging and not modifiable by training patterns, this is it. Our data have shown that masters athletes have youthful, compliant -- 'stretchy'-- hearts that fill well at low pressures. However, no amount of training was able to prevent the slowing of relaxation."

Many people simply presume that this decline in heart rate is the cause of age-related VO2 max decline. But the reality appears to be considerably more complex. What counts is the ability of the heart to pump blood, and that's comprised of two factors: heart rate and stroke volume (the amount of blood pumped with each beat). In a 2001 study that didn't get as much attention as it deserved, Levine and colleague Darren McGuire had a unique opportunity to study the effect of 30 years of aging on a small cadre of ordinary individuals. (Other long-term studies had involved elite athletes, a group that might not be representative of the rest of us.)

The study began in the 1960s, when five college students volunteered for three weeks' total bed rest. Their catastrophic declines in aerobic conditioning are a major reason why nurses now prod surgical patients out of bed as quickly as possible. But before being put to bed, the young men were subjected to the type of testing normally reserved for elite athletes.

Thirty years later, McGuire and Levine realized they could retest the same men in their early 50s. The follow-up study revealed lots of things, not the least of which was that the intervening decades hadn't been as hard on their VO2 max values as the three weeks' bed rest. Of greater interest, though, was the discovery that the men's stroke volumes had increased. It was already known that this happens, as the heart enlarges to force blood through age-stiffened arteries. But nobody anticipated the magnitude of the effect. It turned out to be more than enough to compensate for the decline in maximum heart rate. A 50-year-old's heart might not beat as rapidly as it once did, but it can pump at least as much blood per minute.

What this means is that changes in VO2 max aren't entirely driven by changes in the heart. If the heart is delivering as much oxygen as before, but VO2 max is declining, it must be that the muscles are becoming less adept at using it.

What precisely is going on is a subject of considerable dispute. Partly, it's simply that people lose muscle mass with age. Smaller muscles use less oxygen.

But other factors are probably also involved. Perhaps aging muscles have fewer capillaries to supply them with blood. Maybe they're less able to call for blood when they need it. Or perhaps their cells have fewer mitochondria (the powerhouses in which oxygen is used). Perhaps their arteries become increasingly clogged or inelastic.

A more complex theory comes from exercise physiologist Tim Noakes, who argues that for each stride, the aging brain may simply be using a lower fraction of the available muscle cells. Physiologists have long known that for any given movement, our nerves recruit only a fraction of each muscle's fibers, letting the others rest. In the latest edition of Lore of Running, Noakes suggests that as we age, our nervous systems may become more cautious about protecting our muscles from overload. (This is, however, an extremely controversial theory that has provoked outspoken dissent from other scientists.)

Whatever the cause, the solution is fairly straightforward: run.

Richard Brown is a 71-year-old exercise physiologist and coach from Eugene, Ore., whose trainees have included Suzy Favor Hamilton, Vicki Huber and Mary Slaney. He believes that the secret to holding onto as much VO2 max as possible is simply the old Lydiard approach: run, run, run. "It's just moderate-paced work, where you're going at least 60 minutes," he says, though he adds that masters runners may want to go this far only two or three times a week. And he adds, "Eat really good foods."

Others believe speed work factors into the mix (reducing the number of longer runs). "Train fairly hard at your 2-mile or 5K pace at least once a week, where you're running your heart rate up to 98 percent of maximum," says Portland, Ore.-based coach Bob Williams. "I'm a real believer in that."

McMillan concurs. "These are great things to include in your training program," he says of 5K-paced workouts. "I wouldn't say year-round, but frequently."

He also recommends racing frequently, perhaps once every three to six weeks, particularly 5Ks. "That's a great VO2 max workout in and of itself. The more I look at masters runners, the more I think you've got to keep racing. You almost go back to George Sheehan. He was the king of racing every weekend. It doesn't have to be 100 percent, and you can't do long. The more 5Ks and 8Ks you can do, the better. This is completely different from what you'd advise for a 23-year-old who wants to go to the Olympics."

Flexibility

One of the people involved in McGuire and Levine's study was Gregg Hill. At 20, Hill was a college sophomore who could do a 4:45 mile -- no threat to win the Olympics, but no slouch, either. At the end of the follow-up study's intensive training, his VO2 max had been restored ... but not the 4:45 mile. Clearly, aerobic capacity isn't the only factor affecting masters performance. "What determines speed on the track is different from VO2 max," Levine says.

I talked to Hill in 2005, a few years after the follow-up study had come out. He thought the missing factor was the youthful elasticity of his tendons. In support, he cited Steven Vogel, a biologist at Duke University and author of Prime Mover: A Natural History of Muscle, who claims that much of a runner's propulsion comes from energy carried over from the previous stride via the elasticity of stretched tendons. "My guess is that in older people, the tendons are less efficient," Hill said.

Also cutting into your speed is a simple loss of range of motion -- a problem most runners have faced since youth but which intensifies with age.

Part of the difficulty is the typical middle-aged lifestyle. McMillan notes that many masters-age runners spend a lot of their work lives sitting at their desks or in meetings. "We've risen to a level [in our jobs] that can be bad for us," he says. "We're doing a lot of things that don't have us moving. That's the worst thing we can do from a flexibility standpoint."

"Once the muscles start to get tight, you're limiting your power base," adds Williams. "You're not going to be able to move as smooth and efficiently."

The solution is stretching. Not the static stretches that most of us who've been running long enough to have entered the masters ranks grew up on (although those have their place), but the new breed of dynamic stretches.

Not that the stretches have to be all that newfangled; many of the things we used to do in grade school, such as jumping jacks and alternate toe touchers still work, says Brown. The idea is to get blood flowing through the connective tissues, best done by stretching them dynamically before the workout, and statically afterward. "It doesn't have to be a lot," Brown says. And, he notes, it's better to do it consistently for a few minutes each time than to make erratic efforts at more comprehensive routines.

Brown himself often stretches in his post-workout clean-up. "I do seven static stretches in the shower. I've done that for 20 years and I think it's helped."

Williams generally has runners do 15 to 20 minutes of drills while warming up. "Static stretching can be helpful, but dynamic movement is more valuable," he says. In particular, he says, dynamic exercises should focus on calves, hamstrings and hips.

But stretching isn't the only thing that can help retain or restore flexibility. "Use a foam roller four to five days a week," Williams says. "Or get a massage every week or two. The foam roller seems to be the primary tool I've found that keeps competitive runners healthy."

Alternatively, if you want to retain flexibility but don't want it to feel quite so regimented, Williams suggests trying some other sport that works your range of motion. Williams suggests tennis, but pretty much anything is better than nothing, even golf. "There are a lot of things you can do," he says. "You don't need a gym."

McMillan agrees. Experiment with different types of flexibility training, he says. "As a masters runner, you've got to investigate and find the methods that work."

Declining Muscle Power

Another indisputable side effect of aging is a decline in muscle mass. According to the American College of Sports Medicine, muscle strength and mass begin decreasing at age 40, with the process speeding up after age 65 or 70. Of particular concern to runners, the loss generally occurs fastest in the lower body.

The rate of loss appears to be faster for fast-twitch fibers than for slow-twitch. That's a greater problem for sprinters than for distance runners, but it should be of concern for everyone because it's possible to lose all of your fast-twitch fibers. And when that happens, nobody knows how to get them back.

Scott Trappe, director of the Human Performance Laboratory at Ball State University in Muncie, Ind., was the head of the team that made this discovery. The likely reason, he said at the time, is changing lifestyles. As people age, particularly into their 70s and 80s, they stop doing the high-intensity activities that call for fast-twitch fibers. The result is that these fibers atrophy until they're gone ... permanently.

"The body is going to react to demands," adds Brown. "If you don't demand it any more -- if you think, 'I'm too old to do this, and I'm strong enough anyway,' then you'll start to lose muscle mass."

The solution is vigorous weight-training: the type that gives the same type of "burn" younger athletes seek, albeit at whatever lower weight you can now handle. Fancy health club machines aren't necessary. Rubber tubing, free weights, stretchy bands, calisthenics: any of those can help. "As long as you're doing something two or three days a week to push yourself to a point where you're saying, 'This is starting to get pretty hard,'" Williams says.

Adds McMillan: "The best masters runners never stop. They don't have big down times. They seem to be always training and racing. That may help. The initial research was showing that if you just keep with it, you can reduce that loss of muscle composition."

Slower recovery and healing rates

None of these approaches works if you push too hard, too often. "All the evidence I read doesn't suggest that you can actually slow the aging process," Noakes once told me. "In contrast, I think you can accelerate the aging process if you overdo the exercise."

For younger athletes, he thinks overdoing it is running more than about two hours a day. But many masters runners find that it takes longer than it once did to recover from workouts and races. Lots of factors may be involved, but the simplest to understand is at the cellular level, where tissue repair and replacement simply don't occur as rapidly as they once did.

What this means is that as you age, you may have to experiment with changing your workout pattern. When Carlos Lopes of Portugal won the Olympic marathon at age 37, then went on to win the Rotterdam Marathon at age 38 with a new world record of 2:07:12, Alberto Salazar asked him what he did differently at that age. "Carlos was definitely at an age where most people start having to make adjustments," Salazar says. "He told me that his main adjustment had been to reduce the frequency of his hard workouts. These workouts, he said, still needed to be as intense as ever; he simply allowed more recovery time between them."

McMillan agrees. Masters runners need to do every type of workout that younger runners do, but they may need to alter their schedules. And they may need to allow more time to adapt. "We are so engrained with Tuesday-Thursday [speed], Sunday long run," he says. "You almost have to throw that out the window and start looking at what's going to help. That's going to be different for every runner."

Masters runners also need to be careful to allow enough recovery time after races. "It used to be a race on Saturday, long run on Sunday; no problem," McMillan says. "When you get older, that may not be the best routine."